Five phase stepping motor

ABSTRACT

In the homopolar five phase stepping motor disclosed, five stator windings are distributed on u groups each having five main poles and coacting with a permanent magnet rotor. Each pole has n+1 pole teeth. The five stator windings are connected in series to form a loop having five connecting points. A control switches five transfer switches having an armature connected to a connecting point, between a positive and negative potential so as simultaneously to energize four windings and short-circuit the fifth. The control means then shifts the short-circuited condition to other windings in cyclical sequence while energizing the remaining four windings at any time. The pole divisions exhibit the relationships

United States Patent 91 Heine Feb. 11, 1975 FIVE PHASE STEPPING MOTOR[75] Inventor: Gunter Heine, Lahr, Germany [73] Assignee: Gerhard BergerFahrik Elektrischer Messgerate, Lahr, Germany 22 Filed: July 16,1973

21 App1.No.:379,223

[30] Foreign Application Priority Data Primary Examiner-G. R. SimmonsAttorney, Agent, or Firm-Toren, McGeady and Stanger [57] ABSTRACT In thehomopolar five phase stepping motor disclosed, five stator windings aredistributed on 14 groups each having five main poles and coacting with apermanent magnet rotor. Each pole has n+1 pole teeth. The five statorwindings are connected in series to form a loop having five connectingpoints. A control switches five transfer switches having an armatureconnected to a connecting point, between a positive and negativepotential so as simultaneously to energize four windings andshort-circuit the fifth. The control means then shifts theshort-circuited condition to other windings in cyclical sequence whileenergizing the remaining four windings at any time. The pole divisionsexhibit the relationships r,,=n 'r,+ozia= (K+0.6) 1,, =n 1', Bi [3 =1(K' 0.6) The ratio of the rotor tooth widths to stator 2 widths at theouter diameter of the rotor is equal or smaller 20 Claims, 31 DrawingFigures PAIEMEB EBI H SW20; 8 3.866.104

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FIVE PHASE STEPPING MOTOR REFERENCE TO RELATED COPENDING APPLICATIONThis application is related to the copending application of GiinterHeine, Carsten Driige, and Bruno Borgononovi, Ser. No. 294,787, filedOct. 4, I972, entitled FIVE PHASE MOTOR STEPPING SYSTEMS, and assignedto the same assignee as the present application. The subject matter ofthat application is hereby made a part of the present application as iffully recited herein.

BACKGROUND OF THE INVENTION This invention relates to stepping motorsand particularly to five phase stepping motors operating on thehomopolar principle.

Motors utilizing this principle in their operation can be constructed ina relatively simple manner and achieve very small stepping angles.Customarily, such motors utilize a two phase construction with 2 X 4windings. However, presently known homopolar motors exhibitsubstantially smaller efficiencies than heteropolar motors. They arealso subject to several unavoidable resonance areas, at which the motorscan readily fall out of step in the absence of auxiliary externaldamping arrangements.

An object of this invention is to improve stepping motors.

Another object of this invention is to improve the efficiency or outputof such five phase stepping motors.

Another object of this invention is to obtain large stepping frequenciesat small stepping angles.

Yet another object of this invention is to assure satisfactory andstable stepping behavior at very large start and stop frequencies.

SUMMARY OF THE INVENTION According to a feature of the invention, theseobjects are obtained, in whole or in part, in a multiphase steppingmotor ofthe homopolar type, with av permanent magnet rotor, five statorwindings distributed on small u groups each having five main poles, eachof the main poles having small n- I pole teeth, a five phase controlcircuit controlling all the groups and simultaneously energizing fourphases and short-circuitin g the fifth and then shifting theshort-circuited condition to the other phases in cyclical sequence whileenergizing the remaining four phases at any time, the pole divisionhaving the relationship wherein 1-,, is the pitch between poles, 1-,, isthe pitch between adjacent poles of adjacent groups, 1', is the pitchbetween teeth, a is the pitch between adjacent teeth of adjacent polesand B is the pitch between adjacent teeth on adjacent groups, the ratioof the rotor tooth width to the stator tooth width at the outer diameter of the rotor being equal to or smaller than unity, and the numberof rotor teethT, u(5n 4K K' 3), where n, K, and K are whole numbersgreater than or equal to zero.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become evident fromthe following detailed description when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematicsectional view of a stepping motor embodying features of the invention;

FIG. 1' is a somewhat schematic representation of details of a stator ofthe motor in FIG. 1 wherein n 3, K=l, K 3, and u= 2;

FIG. 2 is a schematic diagram illustrating the windings of a stator inFIG. 1, wherein u 2;

FIG. 3 is a schematic circuit diagram illustrating the principle of acircuit Fl wherein windings corresponding to the windings of FIG. I areenergized, and which corresponds to the winding system used in FIG. 2;

FIG. 4 is a schematic diagram illustrating the principle of anothercircuit F2, wherein windings comparable to those shown of FIG. 1 aresuitably energized;

FIG. 5 is a somewhat schematic sectional illustration of another motorembodying features of the invention;

FIG. 6 is a schematic section illustrating still another motor embodyingfeatures of the invention;

' FIG. 7 is a table indicating the number of rotor teeth T, fordifferent values of n, K, and K when u 2 and m 5;

FIG. 8 is a schematic representation of a five phase stepping motorsystem described in the copending application Ser. No. 294,787;

FIG. 9 is a schematic representation of a stepping motor system alsodescribed in the copending application Ser. No. 294,787;

FIGS. 10a through 102 are voltage-step diagrams illustrating theswitch-actuating sequence, and hence the voltages at the correspondingnodes, at the varying switches in FIGS. 8 and 9 described in thecopending application Ser. No. 294,787;

FIGS. 11a through lle illustrate the magnetic polarizations of thewindings in the system of FIG. 8 when the switches are shiftedstep-by-step as shown in FIG. 10 as described in the copendingapplication Ser. No. 294,787;

- FIGS. llf through 11 j illustrate the magnetic polarities of thefive-stator windings in FIG. 9 when the switches are operated as shownin FIG. 10 to produce the corresponding node voltages as described inthe copending application Ser. No. 294,787;

FIGS. 12a to 12f are graphic diagrams illustrating the relationships ofthe magnetizations of the stators and rotors in FIG. 9a when energizedaccording to the diagram of FIGS. 10a through We as described in thecopending application Ser. No. 294,787;

FIG. 13 is a logic diagram for forming the switches of FIGS. 8 and 9 inthe copending application.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1, the motor has fivestator windings which may, for example, be applied on 10 5 X u radiallyarranged stator main poles l with one or several pole teeth 2.

The stator body is composed of punched and superimposed sheets orplates. According to an embodiment, it is composed of one or severallayer packets. According to an embodiment of the invention, the mainpoles 1 have n 1 individual poles 2 wherein n is a whole number equal toor greater than zero.

In the embodiment of FIG. 1, two main pole windings are connected foreach phase in the same winding sense or direction. According to oneembodiment of the invention, this is accomplished by a seriesconnection. According to another embodiment of the invention, this isaccomplished as shown in FIG. 2 by a parallel connection.

The thus formed five phase windings are connected to each other to forma closed pentagon as shown in FIG. 2. The resulting junction points areconnected with the five mechanical or electronic reversing switchesthrough 9 and with the current supply E as shown in FIG. 3.

In the usual manner, the rotor is composed of a central magnet which ismagnetized in the axial-direction. Tangentially toothed pole caps orpole shoes 3 of soft magnetic material carry the magnetic flux lines ofthe central magnet. As shown in FIG. 1', the teeth 4 of the two polecaps or pole shoes are tangentially offset relative to each other by onehalf-pole division.

According to an aspect of the invention, the following are of criticalimportance in the construction of the motor. The stator poles of FIG. 1must be related as follows:

The number T, of rotor teeth thus abide by the general relation T,= u(5n4K +K 3).

The stepping angle is thus d), 360/2mT,

In the above, u is the number of pole groups distributed on the statorcircumference, m is the phase number, n, K, and K are whole numberswhich are chosen on a practical basis. They influence the size of thestepping angles and the winding technique. For large motor units, it isadvantageous to chose small stepping angles considering the rotor momentof inertia. On the basis of the assembly of the winding, the values Kand K should not be too small. However, on the basis of efficiency laws,these values should not be made too large.

FIG. 7 is a table indicating the number of rotor teeth T for differentvalues of n, K, and K when u 2 and m 52 Generally, in a motor embodyingfeatures of the invention, the main pole distances and group distancesare not equal. Only in the special case where K K and a [i are thesedistances equal. Under those circumstances distribution of the main poledistances over the entire circumference will be equal as shown in FIGS.5 and 6.

Included among the critical aspects of the invention, the statorwindings 30, for example those designated 10 to 14 and 15 to 19, shouldbe switched in such a manner that the pole sequence alternates at thestator main poles as shown in FIG. 2. This means that one north polewill always follow a south pole. According to the invention, this isachieved without significant expenditure for electronic equipment withthe five phase circuit of the aforementioned copending application Ser.No. 294,787, in which one phase winding always remains unexcited. As aresult, contrary to known homopolar motors, no magnetic coupling of twoadjacent poles occurs for any switching conditions.

The consequence of this is the avoidance of coupling oscillations whichare induced or excited by the control pulses, thereby permitting, anincrease of the stable start-stop frequency of at least a multiple offour to five relative to known motors of the same size. Moreover,regardless of the respective switch positions, the magnetic flux throughthe useful air gap remains concentrated or bundled uniformly at alltimes. Scattering or straight flux is thus largely prevented orminimized. The efficiency or output of the motor is improved by about 50percent.

Another'important aspect of the invention resides in the fact that therotor teeth are trapezoidally-shaped. The ratio of tooth width to toothgap is 1:2 at the outer diameter rotor and approximatedly 2:l at thediameter of the rotor base of the tooth. Tests have demonstrated thatthis maximizes the motor power.

Motors embodying the construction, switching and control of the featuresof the invention, are superior to presently known types of steppingmotors having permanent magnet rotors and otherwise exhibiting this samestructural size.'Disregarding the slightly greater electronic equipmentnecessary for control, this superiority applies to the output andefficiency, the holding momentum, the step stability, the availablesteps per second, the start and stop behavior at large steppingfrequencies, and the lower limit of the stepping angle. Thus, motorsembodying the invention exhibit a substantial technical improvement inthe field of stepping motors.

According to an embodiment of the invention, additional bisection orhalving of the stepping angle is obtainable without changing the motorconstruction by using the control circuit F2 having ten reversingswitches 20 to 29 as shown in FIG. 4. This, of course, involvesadditional expenditures for electronic control equipment.

FIGS. 8, 9, 10a to l0e, 11a to llj, and 12a to and 13 correspond tofigures in the aforementioned application Ser. No. 294,787. Thefollowing refers to these figures for the purpose of describing theoperation in this copending application. 1

In the embodiment of the invention illustrated in FIG. 8, five statorwindings l, 2, 3, 4, and 5 are connected in a series looped to form apentagon similar to the manner in which three windings of a threephasemotor are connected to formm a delta connection. The pentagon connectionproduces five nodes 6, 7, 8, 9, and 10 at the five interconnectingpoints. Five transfer switches S6, S7, S8, S9, and S10 have respectivearmatures connected to the nodes 6, 7, 8, 9, and 10 and serve to connecteach of the nodes selectively either to thepositive or negative terminalof a power source P. During the first step of the stepping motoroperation, the switches assume the positions shown. The characters A andE denote the winding directions of the windings 1, 2, 3, 4, and 5. Thus,in the positions shown during the first step, the winding 1 isshort-circuited and the windings 2, 3, 4, and 5 simultaneously producemagnetizations of the same magnetic polarity, such as north.

FIG. 9 corresponds to FIG. 8. Here, the switches S6, S7, S8, S9, and S10are also shown in the position corresponding to the first step of thestepping motor. These positions are identical to the positions in FIG.9a. However, in the embodiment of FIG. 3b the windings 1, 2, 3, 4, and 5are arranged in the winding order I, 4, 2, 5, and 3. The characters Aand E identify the winding directions, as stated.

The, switches S6, S7, S8, S9, and S form part of a control circuit whichswitches the switches back and forth between positive and negative polesthrough a predetermined cycle. Each stator and rotor is divided intoindividual poles with the stators having an interpolar distance T,between individual adjacent poles. In order to obtain predetermineduniform rotary stepping angles, the rotary displacement between theadjacent stators or rotors within the pole distance T can be (I),l/5T,,, or 2/5 T,,.

FIG. 8 illustrates the wiring for producing an angle of rotation 41, andFIG. 9 illustrates the winding required for producing the angle ofrotation b FIGS. 10a through 10e illustrate the switch positions of theswitches S6, S7, S8, S9, and S10 during a series of steps. It alsoimplicitly represents the voltages appearing at the nodes 6 through 10.

Each of FIGS. 1 1a through 1 1e illustrates the polarity ofmagnetization of one pole in each of the stators ener gized by thewindings 1 through 5 during the first eleven steps in the system of FIG.8. Each of FIGS. 11f through 11j illustrates the polarity ofmagnetization of one pole in each of the stators energized by thewindings 1 to 5 during the first eleven steps in the system of FIG. 9.

FIG. 12a illustrates the position of the stator poles P11, P12,...Pln;P21, P22,...P2n; P31, P32,...P3n; P41, P42, ...P4n; and P51, PS2,...P5nof the respective stators l, 2, 3, 4, and 5 relative to each other andrelative to the rotor poles R1, R2,...during the first step in thesystem of FIG. 90 when energized as shown in FIG. 10 and operating asshown in FIG. 11a. It is assumed here that the stators, which are fixedrelative to each other, rotate relative to the rotor whichis fixed. Forsimplicity, the stators have been designated with the same referencenumerals as the windings which they carry.

FIGS. 12b and 12c illustrate the same relationships between the statorpoles and rotor poles as FIG. 12a, but for the second and third steps.FIGS. 12d through 12f illustrate the same relationships for the systemin FIG. 9 when energized as in FIG. 10 and operating as Shown in FIG.11b.

As can be seen from FIGS. 8, 9, 11a, and 11b, four windings carrycurrent during each step. That is to say, four stators are energizedsimultaneously. The fifth winding is short-circuited either to thenegative or positive terminal of the voltage source.

Energizing only four out of five windings may appear to produce somedisadvantages. However, it ultimately results in higher efficiency. Ifit is assumed that the static torque characteristics of the individualstators follow a sinusoidal course, excitation of all five stators,produces a characteristic holding moment which is 3.2 times the value ofthe maximum moment of a single stator. However, when four stators aresimultaneously excited, the characteristic holding moment is 3.1 timesthe value of the maximum moment of a single stator. Thus, energizingfour windings instead of five produces a reduction in the holding momentwhich degrades the dynamic performance by only about 5 percent. Thestepping angle and the waviness of the operating torque exhibitsubstantially the same value when four stators are energized as whenfive stators are energized.

However, energizing only four of five stator winding at any one timereduces the required input power approximately 20 percent. As a result,the total efficiency increases 15 percent with about 20 percent lessheating of the motor. Making power comparisons, the motor heating withinan insulation class represents a reference point. Thus, the power andhence the maximum moment of a single stator can be raised about 20percent when only four stators are excited. As a result, circuitsembodying the present system exhibit an approximately l5 percent higherholding moment than circuits energizing all five windingssimultaneously.

The fifth, non-excited winding is always shortcircuited. Thus, theelectromotive force which the permanent magnet rotor induces into theshort-circuited winding during a stepping operation produces a dampingeffect on the motor system. Therefore, at higher stepping frequenciesthe operating torque is again somewhat reduced. However, the degree ofdamping which is relatively low in all electric stepping motorsincreases. This reduces undesirable pendular vibrations of the rotor.

FIG. 13 is a logic diagram for forming the switches in FIGS. 8 and 9.

The term pitch is used herein as the angle between centers or other likeportions of adjacent parts.

The characters 13,, r,,, r,, a and B are defined by their showing on thedrawings.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

l. A five phase stepping motor system, comprising a stepping motorhaving five untapped stator windings connected said stator windingsforming a plurality of connecting points, a permanent magnet rotor,control means connected to said five connecting points for energizingsaid windings, said stepping motor including 14 groups each having fivemain poles, each of said main poles having 11 l pole teeth, said statorwindings being distributed on said groups and poles, said. poles beingdivided in accordance with the relations the ratio of rotor tooth widthsto stator tooth widths at the outer diameter of the rotor being equal toor smaller than unity, the number of rotor teeth T, corresponding to therelationship T u(5n +4K K 3), where 1,, is the pitch of adjacent mainpoles, 1, is the pitch of adjacent pole teeth, a is the angle betweenadjacent pole teeth on adjacent poles, 1', is the pitch between adjacentpoles on adjacent groups, B is the angle between adjacent pole teeth onadjacent groups and n, K, and K are whole numbers equal to or greaterthan 0.

2. A motor as in claim 1, wherein said control means short-circuits oneof said windings while energizing the others of said windingssimultaneously and shifts the short-circuited winding in succession fromwinding to winding while simultaneously energizing the remaining ones ofsaid windings.

3. A motor as in claim 1, wherein said control means include means forconnecting said winding in a pentagonal loop.

4. A motor as in claim 2, wherein said control means include means forconnecting said winding in a pentagonal loop.

5. A motor as in claim 1, wherein said control means connects the statorwinding so that the main poles always exhibit alternating polarity.

6. A motor as in claim 2, wherein said control means connects the statorwinding so that the main poles always exhibit alternating polarity.

7. A motor as in claim 3, wherein said control means connects the statorwinding so that the main poles always exhibit alternating polarity.

8. A motor as in claim 1, wherein said control means energizes each ofsaid windings so that two of successive ones of said windings havecurrent flowing in the same direction while the remainder of thesuccessive windings have currents flowing in opposite directions.

9. A motor as in claim 1, wherein said control means connects thewindings so that, independent of the switching position, two adjacentmain poles always have the same polarity while the others, havealternating polarities.

10. A motor as in claim 1, wherein said pole teeth have trapezoidalshapes, the ratio of tooth width to tooth gap at the outer diameter ofthe rotor being 1:2 and at the tooth root about 2:1.

11. A motor as in claim 3, wherein said pole teeth have trapezoidalshapes, the ratio of tooth width to tooth gap at the outer diameter ofthe rotor being l:2 and at the tooth root about 2:1. I

12. A motor as in claim 1, wherein each main pole has n l pole teeth,the ratio of stator to rotor tooth width being 2:].

13. A motor as in claim 3, wherein each main pole has n l pole teeth,the ratio of stator to rotor tooth width being 2:1.

14. A motor as in claim 1, wherein said control means can switch theindividual windings in series connection and parallel connection.

15. A motor as in claim 1, wherein r, r,

16. A motor as in claim 3, wherein 1,, 13;

17. A motor as in claim 4, wherein -r,, 1,,

18. A motor as in claim 1, wherein a B and at least one of said mainpoles has tooth gaps.

19. A motor as in claim 3, wherein a B and at least one of said mainpoles has tooth gaps.

20. A motor as in claim 14, wherein a B and at least one of said mainpoles has tooth gaps.

1. A five phase stepping motor system, comprising a stepping motorhaving five untapped stator windings connected said stator windingsforming a plurality of connecting points, a permanent magnet rotor,control means connected to said five connecting points for energizingsaid windings, said stepping motor including u groups each having fivemain poles, each of said main poles having n + 1 pole teeth, said statorwindings being distributed on said groups and poles, said poles beingdivided in accordance with the relations Tau p n Tau z + Alpha i AlphaTau z(K + 0.6) Tau p'' n Tau z + Beta i Beta Tau z(K'' + 0.6), the ratioof rotor tooth widths to stator tooth widths at the outer diameter ofthe rotor being equal to or smaller than unity, the number of rotorteeth Tr corresponding to the relationship Tr u(5n +4K + K'' + 3), whereTau p is the pitch of adjacent main poles, Tau z is the pitch ofadjacent pole teeth, Alpha is the angle between adjacent pole teeth onadjacent poles, Tau p'' is the pitch between adjacent poles on adjacentgroups, Beta is the angle between adjacent pole teeth on adjacent groupsand n, K, and K'' are whole numbers equal to or greater than
 0. 2. Amotor as in claim 1, wherein said control means short-circuits one ofsaid windings while energizing the others of said windingssimultaneously and shifts the short-circuited winding in succession fromwinding to winding while simultaneously energizing the remaining ones ofsaid windings.
 3. A motor as in claim 1, wherein said control meansinclude means for connecting said winding in a pentagonal loop.
 4. Amotor as in claim 2, wherein said control means include means forconnecting said winding in a pentagonal loop.
 5. A motor as in claim 1,wherein said control means connects the stator winding so that the mainpoles always exhibit alternating polarity.
 6. A motor as in claim 2,wherein said control means connects the stator winding so that the mainpoles always exhibit alternating polarity.
 7. A motor as in claim 3,wherein said control means connects the stator winding so that the mainpoles always exhibit alternating polarity.
 8. A motor as in claim 1,wherein said control means energizes each of said windings so that twoof successive ones of said windings have current flowing in the samedirection while the remainder of the successive windings have currentsflowing in opposite directions.
 9. A motor as in claim 1, wherein saidcontrol means connects the windings so that, independent of theswitching position, two adjacent main poles always have the samepolarity while the others, have alternating polarities.
 10. A motor asin claim 1, wherein said pole teeth have trapezoidal shapes, the ratioof tooth width to tooth gap at the outer diameter of the rotor being 1:2and at the tooth root about 2:1.
 11. A motor as in claim 3, wherein saidpole teeth have trapezoidal shapes, the ratio of tooth width to toothgap at the outer diameter of the rotor being 1:2 and at the tooth rootabout 2:1.
 12. A motor as in claim 1, wherein each main pole has n + 1pole teeth, the ratio of stator to rotor tooth width being 2:1.
 13. Amotor as in claim 3, wherein each main pole has n + 1 pole teeth, theratio of stator to rotor tooth width being 2:1.
 14. A motor as in claim1, wherein said control means can switch the individual windings inseries connection and parallel connection.
 15. A motor as in claim 1,wherein Tau p Tau p .
 16. A motor as in claim 3, wherein Tau p Tau p .17. A motor as in claim 4, wherein Tau p Tau p .
 18. A motor as in claim1, wherein Alpha Beta and at least one of said main poles has toothgaps.
 19. A motor as in claim 3, wherein Alpha Beta and at least one ofsaid main poles has tooth gaps.
 20. A motor as in claim 14, whereinAlpha Beta and at least one of said main poles has tooth gaps.